It depends on what type of protection is on the disc, and the exact movie release... but dvdfabdecrypter usually works

http://www.videohelp.com/tools?tool=DVDFab_Decrypter

Then, open those files with dvd shrink. If that doesn't work, you may have to run it thru vob blanker to remove the bad vob files.

http://www.videohelp.com/tools?tool=VobBlanker

If that doesn't work, it's going to get a lot more complicated ie manually detecting and deleting bad vob files and restructuring the ifo file.

BTW, what movie is it?